Automatic compression release for internal combustion engine



Dec. 24, 1968 AUTOMATIC COMPRESSION RELEASE FOR INTERNAL COMBUSTION ENGINE Filed Oct. 18, 1967 R. E. PERLEWITZ 2 Sheets-Sheet 1 IIIIITII n- I mvENToR; 1

ATTORNEYS Dec. 24, 1968 R. E. PERLEWITZ 3,417,740

AUTOMATIC COMPRESSION RELEASE FUR INTERNAL COMBUSTION ENGINE Filed Oct. 18, 1967 2 Sheets$heet 2 INVENTOR. 05427 4. P564 :w/rz

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ATTORNEYS United States Patent 3,417 .740 AUTOMATIC COMPRESSION RELEASE FOR INTERNAL COMBUSTION ENGINE Robert E. Periewitz, Mequon, Wis., assignor to Tecumseh Products Company, Tecumseh, MiclL, a corporation of Michigan Filed Oct. 18, 1967, Ser. No. 676,153 Claims. (Cl. 123182) ABSTRACT OF THE DISCLOSURE An automatic compression release mechanism for an internal combustion engine wherein two independently operating valves, preferably self-biasing reed valves, are mounted to respectively control serially connected inlet and outlet ports of a valve chamber which forms part of a compression release passageway connecting the combustion chamber of the engine with a zone of lower pressure, such as the exhaust passage of the engine. The valves are each one-way check valves acting oppositely to one another. The valve controlling the outlet port is normally biased to an open position so that it remains open when the engine is turned over at the relative slow cranking speeds normally used to start the engine to thereby relieve compression and thus facilitate starting of the engine. The outlet valve projects into the gas-flow stream so that it is yieldably flexed to closed position in response to explosive pressure generated in the passageway when the fuel-air charge is ignited in the combustion chamber, thereby sealing the compression release passage after the engine starts.

An object of the present invention is to provide an efficient, reliably and economical valve mechanism for automatically relieving compression in an internal combustion engine when the same is cranked over at starting speed and which automatically seals the compression release passageway in response to the engine firing so that no power loss occurs while the engine is running.

Another object is to provide an automatic compression release mechanism of the above character which is readily adaptable to existing engines and which is easily accessible for cleaning and/or replacement of the parts used therein.

Other objects as well as features and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a top view of the head end of a two-strokecycle internal combustion engine equipped with a compression release of the present invention, the same being shown with the head removed and the cylinder block sectioned through the compression release mechanism.

FIG. 2 is a fragmentary side elevational view of the engine cylinder block with the head and transfer chamber cover removed.

FIGS. 3 and 4 are fragmentary sectional views taken on the lines 3-3 and 44, respectively, of FIG. 2, illustrating the communicating compression release passageways in the valve chamber cover and engine block.

FIG. 5 is a fragmentary enlarged view of the outlet reed valve and associated outlet port structure of FIG. 1.

FIG. 6 is a fragmentary side elevational view of a portion of FIG. 2 illustrating the valve chamber cavity and inlet reed valve with the cover removed from the valve chamber.

' FIG. 7 is a side elevational view of the inside of the valve cover and associated outlet reed valve shown by themselves separate from the block.

FIG. 8 is a sectional view taken on the line 88 of FIG.

1 showing the piston in top dead center position with a portion broken away to illustrate the compression release port in the cylinder wall.

The automatic compression release structure of the present invention may be an add-on to a conventional twost-roke cycle single cylinder engine 10 which has the usual piston 11 (FIGS. 1 and 8) controlling exhaust ports 12 (FIGS. 4 and 8), air inlet ports 16 and transfer ports 14 in the wall 18 of a cylinder liner 20. Generaly speaking, the arrangement consists of a passageway leading from the combustion chamber 22 to a Zone of lower pressure relative to the combustion chamber 22 during the compression stroke of piston 11, such as the crankcake cavity 25 or exhaust passageway 26. This compression release passageway is controlled by two reed valves 30 and 32 mounted in a valve chamber 34 serially connected in the passageway. Reed 30 is adapted to close communication between combustion chamber 22 (FIG. 8) and valve chamber 34 (FIG. 1) when pressure in the exhaust passageway 26 or other relief zone exceeds combustion chamber pressure, reed 30 thereby serving as a one-way back check valve. The other reed 32 is resiliently self-biased normally open so as to relieve compression during cranking of the engine for starting but is responsive to the sharp blast flow through the compression release passageway when the engine fires so as to be rapidly bent to close the valve chamber outlet port 36 (FIG. 5);

As shown in FIGS. 1, 3 and 4, the compression release passageway includes a vent passage 40 which, for example, may be .156 inch in diameter which extends from the cylinder combustion chamber 22 through liner 20 and block 42 to valve chamber 34. Chamber 34 is formed by a cavity 44 in a boss 46 cast integrally on the block which is closed by a cover plate 48 secured by two studs 58 and 52 to boss 46. The vent passage 40 opens into the engine cylinder at a point such that passage 40 will just begin to be covered by the crown edge of piston 11 when the piston has traveled about of its ascent toward its top dead center T.D.C. position (solid lines, FIG. 8). The compression release passageway also includes chamber 34 and outlet passage 36 which opens at one end to chamber 34 and at its other end 54 (FIGS. 3 and 4) to a passage 56 in block 42 which in turn leads to the exhaust passage 26 of the engine. Alternatively, passage 56 can lead to the charge transfer chamber 58 at a point adjacent the transfer ports, which in turn communicate with the crankcase, or passage 56 can lead directly to atmosphere. However, venting to the exhaust passage insures that released gases pass through the mufiler. Venting to exhaust passage or to the crankcase insures that the oil drippings and vented charge are directed to an area where they are least noticeable and least disturbing to the flow of gases from the carburetor. The normally closed back check reed 30 is mounted at one end by a stud 60 on boss 46 to lay flat against the cylinder side of the valve chamber with the free end 62 of reed 30 covering the outlet end of cylinder vent passage 40. Reed 30 is mounted without any preloading, i.e., when in closed position it is in a relaxed condition and does not start developing spring bias until it starts bending as it is forced off its seat 64 by the pressure of a charge being compressed in the engine cylinder during the compression stroke of the piston.

The normally open outlet check reed 32 is secured at one end by a stud 66 to cover 48 with its free end 68 overlying but spaced from the valve chamber outlet port 36 in cover 48, as shown in the 5:1 scale fragmentary view in FIG. 5. The valve seats for both the back check valve 30 and outlet check valve 32 preferably are raised seats. Thus, as best seen in FIG. 5, cover 48 has an annular rim 7!) around the chamber opening of passage 36 which projects from the adjacent surrounding surface 72 of cover 48 so that reed 32 when in closed condition seats only on rim 70 (broken line showing, FIG. 5). By so limiting the area of contact between each reed and its seat, it has been found that a problem of valve sticking is overcome which otherwise would occur if the valve were allowed to contact a large surface covered with products of combustion and oil from the engine.

Reeds 30 and 32 are preferably made from type 420 stainless tempered and polished spring steel strip about .004" thickness and adapted to withstand corrosive atmospheres and temperatures of about 800 to 1000 F.

In operation, when piston 11 is starting its ascent and the engine is being manually cranked for starting, combustion chamber pressure will be at a minimum and equal to or higher than atmospheric pressure which is communicated through the relief passages 26, 56, 54, 36 to valve chamber 24. As piston 11 ascends toward top dead center on its compression stroke, the pressure of the fuelair mixture in the combustion chamber rises above atmospheric pressure, thereby creating a pressure differential which opens reed 30 and causes the fuel-air mixture to flow from combustion chamber 22 to valve chamber 34 via vent passage 40. The gases thus released from the combustion chamber continue on past and around the free end 68 (FIG. 5) of outlet check reed 32 and thence into the cover passageway 36 and are conducted via passages 54 and 56 to the exhaust passage 26. Reed 32 is designed to remain open even when the gas flow across its free end 68 reaches that resulting from maximum engine compression pressure and minimum exhaust passage pressure at or below engine cranking speed. Hence so long as the engine does not fire, compression will be relieved on every compression stroke until piston 11 covers the relief port 40 of the vent passageway. However, outlet check reed 32 closes rapidly onto seat 70 once the fuel-air mixture is ignited and the sharp combustion pressure blast reaches valve chamber 34. At this point piston 11 is starting to cover relief port 40. During the last twenty percent or so of the pistons ascent to top dead center, relief port 40 is closed by piston 11 and remains closed until uncovered again by the piston during the first twenty percent of its descent toward bottom dead center. Once valve chamber 34 has been pressurized by the combustion gases, both reeds 30 and 32 tend to seal their respective ports and thereby retain a high pressure charge of the gases in valve chamber 34 so that both valves 30 and 32 remain closed when the engine is running under its own power.

Preferably, the size and location of relief port 40 and vent passageways provides sufiicient venting on the compression stroke during cranking to reduce the maximum compression pressure by about fifty percent over unrelieved compression pressure, e.g., so that compression pressures will be reduced from about 100 p.s.i. to about 50 p.s.i. at cranking speeds. If the engine does not fire on the compression stroke of the piston, then on the subsequent downstroke of the piston after the same has moved downwardly sufficiently to uncover port 40, the pressure differential across valve chamber 34 will still be in a direction tending to open back check valve 30. Hence, at cranking speed and so long as the engine does not fire, valve 30 will cycle with the engine as described above, closing only when port 40 is covered by the piston. Under these conditions outlet check valve 32 will remain open due to its self-biasing force being greater than the drag forces exerted on valve 32 by the gas flow through chamber 34 at cranking speed, thereby relieving compression to reduce cranking effort and thus facilitate starting.

However, once the engine fires, outlet valve 32 will be closed by the rapid increase of pressure in the valve chamber. The subsequent reduction in combustion chamber pressure as the piston uncovers the exhaust ports on its down stroke will cause back check valve 30 to close soon after valve 32, thereby trapping combustion gases in valve chamber 34 at a pressure somewhere between peak compression pressure and peak combustion pressure, e.g., on

4 the order of 200250 p.s.i. Valves 30 and 32 then remain closed while the engine is running except for a small amount of leakage of combustion gases past valve 30 into chamber 34 to make up for small leakage losses from chamber 34 via valve 32.

When the engine is shut off the slight leakage permitted by valve 32 as well as the drop in temperature of the gases in chamber 32 as the engine cools off causes the pressure in chamber 34 to drop sufiiciently in a period of about 10-20 seconds so that the self-biasing force of valve 32 overcomes the force exerted by the gases and pops valve 32 off its seat and returns it to its normally open position as shown in FIGS. 1 and 5. Chamber 34 then immediately returns to atmospheric pressure, and if the engine is now once again cranked, starting effort will again be reduced as described above. If desired, the leakage rate from chamber 34 may be increased by providing a calibrated restricted orifice in cover 48 so as to bypass valve 32 with a slow leak, or such a leakage orifice may be provided directly in reed 32 in the portion thereof covering port 36 in the closed position of reed 32. Although some leakage is thus desirable past valve 32, valve 30 is operable to keep such leakage to a minimum so that valve 32 does not suffer damage in the manner of a leaky exhaust valve when the engine is running.

I claim:

1. In an internal combustion engine having a cylinder and piston defining a variable volume combustion chamber, an automatic compression release mechanism comprising a passageway communicating at one end thereof with said combustion chamber and at the other end thereof with a zone in which the pressure is lower than the pressure in said combustion chamber during the compression stroke of said piston, a valve chamber having an inlet port and an outlet port serially connecting said chamber in said passageway, a first one-way valve controlling said inlet and closing the same when valve chamber pressure exceeds combustion chamber pressure, and a second one-way valve operable independently of said first valve controlling said outlet and tending to close the same when valve chamber pressure exceeds the pressure in said zone, said second valve being resiliently biased to an open position spaced from said outlet and projecting into the gas flow stream between said inlet and outlet so that said valve is driven to closed position in response to explosive pressure generated in said passageway when a fuel-air charge is ignited in said combustion chamber, said first valve and second valves being both biased to their respective closed positions in response to a pressure build-up in said chamber sufiicient to maintain said second valve closed whereby both of said valves tend to be maintained in closed position when the engine is running,

2. The combination set forth in claim 1 wherein said one end of passageway comprises a port in the Wall of said cylinder located relative to said piston such that said port is covered by said piston when the same has traveled approximately eighty percent of its asecnt toward top dead center from bottom dead center.

3. In an internal combustion engine having a cylinder and piston defining a variable volume combustion chamber, an automatic compression release mechanism comprising a passageway communicating at one end thereof With said combustion chamber and at the other end thereof with a zone in which the pressure is lower than the pressure in said combustion chamber during the compression stroke of said piston, a valve chamber having an inlet port and an outlet port serially connecting said chamber in said passageway, a first one-way valve controlling said inlet and closing the same when valve chamber pressure exceeds combustion chamber pressure, and a second oneway valve controlling said outlet and tending to close the same when valve chamber pressure exceeds the pressure in said Zone, said second valve being resiliently biased to an open position spaced from said outlet and projecting into the gas fiow stream between said inlet and outlet so that said valve is driven to closed position in response to explosive pressure generated in said passageway when a fuel-air charge is ignited in said combustion chamber, said first and second valves comprising first and second resilient reeds each rigidly connected at one end to said engine and having a free end opposite said one end disposed to open and close the associated port of said valve chamber.

4. The combination set forth in claim 3 wherein said outlet comprises a port having a raised rim encircling said port with a flat valve seat formed on said rim of relatively narrow radial dimension relative to the diameter of said outlet port, said free end of the second reed overlying and contacting said seat in closed position and extending generally perpendicular to the axis :of said rim such that reed is spaced clear of the wall of said valve chamber in closed position except for the portion of said free end of said second reed contacting said rim valve seat.

5. The combination set forth in claim 3 wherein said valve chamber comprises a cavity in the exterior of said engine and a cover removably secured to said engine and closing said cavity, and wherein said passageway com prises: a straight hole extending from said cylinder to an opening in a surface of said cavity, the space in said cavity, a passage in said cover extending from said outlet port to a port in the face of cover disposed against the engine and a passage in said engine extending from said cover port to the exhaust passage of said engine.

References Cited UNITED STATES PATENTS WENDELL E. BURNS, Primary Examiner.

US. 01. cR. 123 105, 

